Cows graze in a field next to one of the old nuclear reactors (right). An older nuclear reactor site, operated by General Electric, sits off highway 84 in the Sunol, Calif. area.

Cows graze in a field next to one of the old nuclear reactors (right). An older nuclear reactor site, operated by General Electric, sits off highway 84 in the Sunol, Calif. area.

Photo: Brant Ward, The Chronicle

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General Electric owns much of the land surrounding the facility and has plenty of No Trespassing signs posted. An older nuclear reactor site, operated by General Electric, sits off highway 84 in the Sunol, Calif. area. less

General Electric owns much of the land surrounding the facility and has plenty of No Trespassing signs posted. An older nuclear reactor site, operated by General Electric, sits off highway 84 in the Sunol, ... more

Photo: Brant Ward, The Chronicle

Image 3 of 4

Cows graze in a field next to some old nuclear reactors, which are the rounded steel structures. A water tank sits above right. An older nuclear reactor site, operated by General Electric, sits off highway 84 in the Sunol, Calif. area. less

Cows graze in a field next to some old nuclear reactors, which are the rounded steel structures. A water tank sits above right. An older nuclear reactor site, operated by General Electric, sits off highway 84 ... more

Photo: Brant Ward, The Chronicle

Image 4 of 4

Bay Area has couple of small nuclear reactors

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Not far from Pleasanton, in a grassy valley grazed by cows, lies a nuclear reactor that the Bay Area keeps forgetting.

Another sits 17 miles away in San Ramon.

By the standards of the nuclear industry, both reactors are tiny. The small amounts of energy they generate don't flow onto California's power grid. Instead, operators use the neutrons from each reactor to peer inside solid objects, in a process similar to X-ray imaging.

Thirty-six "research and test" reactors are scattered throughout the United States, often on college campuses. Four are in California. They rarely draw attention except from the researchers, companies and government agencies that rely on them.

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That may change, at least briefly, due to Japan's nuclear crisis, in which partial meltdowns and radiation releases at a quake-stricken nuclear plant have forced authorities to evacuate the surrounding area. Small test reactors, after all, operate on similar principles to their much larger cousins, using uranium fuel rods held close to one another to generate fission.

But they are also different in key aspects of their design, differences that operators say make meltdown virtually impossible.

Safety features

For example, the center's reactor can't sustain a nuclear reaction if the water surrounding the fuel rods leaks out, said Turner. It also can't sustain the reaction if the temperature rises above 120 degrees. Other small reactors have similar safety features.

"The hotter it gets, the more it poisons its own reaction," said Sandra Warren, general manager of the Aerotest Operations facility in San Ramon.

Indeed, the most common type of test reactor - called TRIGA, for Training, Research, Isotopes, General Atomics - was designed to be safe enough that university students couldn't screw it up. Nuclear engineering students often train on the small reactors before landing jobs at big commercial power plants.

Still, the test reactors sometimes cause controversy. A 2008 report from the U.S. Government Accountability Office found that reactor owners and federal regulators had not sufficiently studied the ways that terrorists could attack the facilities.

And while Bay Area residents tend to forget about the reactors in their midst, some local environmentalists have long questioned whether Vallecitos could be damaged by earthquakes.

"There are huge risks in the Tri-Valley area, and throughout the Bay Area, that modern science calculates are much more severe than people thought when these facilities were built," said Marylia Kelley, executive director of the anti-nuclear group Tri-Valley CAREs (Communities Against a Radioactive Environment).

Vallecitos history

Vallecitos has a longer, more illustrious and more contentious history than most small nuclear facilities.

Among the hills near the Sunol Grade, Pacific Gas and Electric Co. and General Electric Co. built the first commercially owned nuclear plant to supply power to the general public. The Vallecitos Boiling Water Reactor began operating in 1957, generating about 5 megawatts of electricity. (For comparison, PG&E's Diablo Canyon nuclear power plant near San Luis Obispo generates about 2,200 megawatts.)

Although PG&E used the power from Vallecitos, the boiling water reactor largely served as a way for GE to test components and systems for the larger commercial plants to come. The company took it out of service in 1963.

But the Vallecitos site had other, smaller reactors as well. One of them, which made radioactive isotopes used in medicine, was closed by federal regulators in 1977, after the U.S. Geological Survey reported that a fault line might run closer to the facility than previously suspected.

That triggered a long, fierce fight between GE and local environmentalists who feared that an earthquake along the Verona Fault could seriously damage the reactor. The Nuclear Regulatory Commission finally gave GE permission to restart the reactor, but the company in 1985 decided not to do so, saying that competitors in the medical isotope business had seized all of GE's former market share.

Still, the company continued to run one last reactor at Vallecitos. Generating just 100 kilowatts, the reactor performs neutron radiography, using neutrons to create images of the interior of objects.

Critics linger

Although forgotten by many, Vallecitos still has its critics. Their focus often isn't on the reactor itself. Rather, they worry about the used fuel rods that owners of commercial nuclear power plants ship to Vallecitos for study. Vallecitos has "hot cells," places for handling radioactive material such as spent fuel rods.

The rods are shipped to Vallecitos by truck. Once examined, the used nuclear fuel is stored on site, in a chemically stabilized form. Turner said Vallecitos has taken in about 300 to 350 kilograms of spent nuclear fuel - or about 660 to 770 pounds - over the years.

"You're storing nuclear waste within feet of a fault line," Kelley said. The possibility of a highway accident involving a shipment of used fuel rods also troubles her.

"Anytime you put spent nuclear fuel on the highway with station wagons and soccer moms, there's a risk," Kelley said.

Turner said the storage facility, as well as the reactor, can withstand earthquakes. And the fuel rod shipping containers must survive tests that involve dropping the containers from a 10-foot height and subjecting them to a diesel-fueled fire.

The San Ramon reactor also has a long history, receiving its operating license in 1965.

Helping NASA

It too specializes in neutron radiography. NASA used its imaging for both the Apollo moon-shot program and the space shuttle.

But the reactor's future is up in the air. The parent company that owns Aerotest is looking for someone to buy the facility, and Aerotest shut the reactor last fall. Several potential buyers have expressed interest, Warren said. But the Nuclear Regulatory Commission, she said, wants to make sure that whoever buys it has the resources to pay for decommissioning the facility, whenever that occurs.